Put Options. They're less risky than shorting, and have similar upsides. The major difference is that if the price goes up, you're just out the underwriting price. You'll also need to know when the event will happen, or you risk being outwaited.
More traditionally, an investor would pull their money out of the market and move into Treasury bonds. Recall that when the market tanked in 2008, the price of treasuries jumped. Problem is, you can only do that trade once, and it hasn't really unwound yet. And the effect is most pronounced on short term treasuries, so you have to babysit the investment.
Because of this, I think some people have moved into commodities like gold, but there's a lot of risk there. Worst case scenario you have a lot of shiny metal you can't eat or use.